Boris Johnson threatened to suspend a G20 policing meeting after members of the public heckled officers. Photograph: Dan Kitwood/Getty Images

Boris Johnson today threatened to suspend a public meeting about the policing of the G20 demonstrations after senior members of the Metropolitan police were barracked by members of the public.

The London mayor stepped in after the officers were repeatedly heckled as they gave evidence to the Metropolitan police authority (MPA) in the chamber at City Hall.

His patience snapped when Chris Allison, the assistant Met commissioner who submitted a report on the "complex" police operation, which had taken three months to plan, attempted to clarify events on the day of the G20 summit.

Some protesters chanted "Ian Tomlinson" – the man who died at the demonstrations shortly after being hit by a police officer – while others wore t-shirts with slogans reading: "No cover-ups".

The protesters, in the chamber's public gallery, were infuriated by the police officers' defence of the use of "kettling" tactics – holding demonstrators in one place – and jeered claims that the Met was a "world leader" in policing.

Johnson, who completes his first year in office as the London mayor today, used his position as the MPA chair to threaten to clear the chamber.

"I think it would be satirical if this important session was disrupted by protesters itself," he said.

"It is sensible to continue our discussion of what went on at G20 for the elucidation of not just people in this chamber, but for millions of people across the country who deserve to hear from the officers here.

"I think it is completely wrong that a tiny minority in this chamber are seeking to disrupt this process and make it impossible for millions of others to get to the bottom of it."

Tim Godwin, the acting deputy commissioner of the Met police service gave evidence alongside Allison in the absence of the Met police commissioner, Sir Paul Stephenson, who is recuperating after an operation to have his appendix removed.

They said the conduct of a tiny minority of officers should not deflect from the performance on the day of the majority of the force – a view echoed by Johnson.

The police account of operations on the day of the protests said that, despite the "exaggeration of the potential violent disorder in the media coverage", officers had been briefed to remain "calm and restrained".

Discussions about media coverage in the run-up to the G20 summit prompted one member of the public to shout: "You caused the violence."

He told the meeting: "Everybody in London and in the country has of course been horrified by some of the images of what happened, in particular to Ian Tomlinson.

"His family need answers, and they need answers urgently, and it is right that there should be a series of Independent Police Complaints Commission inquiries into what happened.

"I think Sir Paul has done absolutely the right thing in calling in Her Majesty's Inspector of Constabulary to review tactics.

"But I hope members will agree that it is clear that the overwhelming majority of police officers in London today and indeed at the G20 are doing a fantastic job."

Two weeks before the demonstration, Johnson used his Telegraph column to condemn "anti-capitalist crusties"

It emerged during the meeting that an officer who had made an "inappropriate" comment about Tomlinson on a social networking site had resigned.

John Hayter, a 49-year-old member of the royal protection unit, stepped down after he wrote on Facebook: "I see my lot have murdered someone again. Oh well, shit happens."

In a statement, the Met said: "The Metropolitan police service will not tolerate any of its employees making inappropriate comments via the internet.

"The Metropolitan police service makes its position clear on employees' use of blogging sites within its standard operating procedures.

"If any employee is identified as contributing material that is racist, homophobic, sexist, defamatory, offensive, illegal or deemed inappropriate, they may be subject to disciplinary procedures."

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